The 51515 verses whatever short filter you want to test.
If you want to see it for yourself you just need two gauges. One in the port at the back of the intake and one in the port on the end of the right angle adapter. Start with whatever filter you have on there and read the pressure difference between the two gauges. Then switch to the other filter and do the same. The one with the least pressure drop across the filter is the least restrictive.
Its easier on a dyno because you can data log the pressure curves and compare the two but you can do it in the car.
To find the difference between the right angle adapter and the filter bolted to the block would be a bit more difficult to do. There is nowhere to put a gauge down at the filter when it’s screwed to the block. That is where a dyno (or an in car data logger) would make it easy. You could test with a short and long filter on the block and a short and long filter on the right angle adapter and then you’d know exactly what the best way to mount the filter is.
Of course, using dyno time to sort that out can get expensive. And I have not done the latter test since I don’t ever screw the filter to the block. Maybe when I get independently wealthy I can spend some money on dyno testing and check out both ways. Until then, I use the right angle adapter and the longest filter that will fit in there.